Fractional distillation



Feb. 4, 1936. E. w. GARD FRACTIONAL DISTILLATION Filed May 21, 1952 y INVENTOR. Ear/e VV. Gard v BY ATTORNEY s invention .relates a process and apparae r iractionating hydrocarbon. oils, particu larly petroleum.

This invention relates particularly to the Withdrawal of side cuts from a main ractionating column and the exhausting and separate fractionation of the withdrawn cuts in an auxiliary rec tirying column, to produce fractions oi improved duality.

Heretofore, when a limited quantity of a hydrocarbon fraction having a denite boiling point range was desired, it has been common practice to Withdraw from the proper intermediatc point in a main fractionating column a porn tion of the descending reflux oil. This oil before removal from the main fractionating column is hausting column to remove the low boiling point components and yield therefrom a residual cut having the said desired boiling point range. The

said removed low boiling point vapors have, in

the` past, either been returned from the exhaust ing column to a later stagev of the main fraction-.

ating column, or run directly to the final condensing system or separately condensed. 4"ilhis has resulted, in the nrst case, inpverloading the later stages of the main fractiona'ting column when steam or other heating vapors are used in the exhausting section; in the second case has resulted in the contamination of the overhead condensate from the main column, with the heavy, high boiling ends which are carried over with the vapors from the auxiliary exhausting column; and in the third case has resulted in the necessity of separately refractionating this con densate with the attendant costly' extra equipment and loss oi heat.

The above enumerated disadvantages have been obviated by this invention.

ln' accordance with 4this invention a liquid traction is withdrawn from an intermediate point in a main fractionating tower and yidthout cooln ing, is stripped oi its low boiling components i an auxiliary exhausting column, countero ru the traction. The stripped bottom" il' i'roi'n this exhausting colinnn cons tcrmcdlatc fraction oi desirable high. pen l tercurrent contact with reflux in an auxiliary fractionating column before being condensed. The remaining fractions and the rei-lux formed in` the auxiliary ractionating system are trapped and returned to an early stage in the main frac= ticnating tower for .continued treatment. The overheadl vapors of the auxiliary fractionating column are withdrawn to a common iinal con denser or separate condenser.

The object or this invention is, accordingly, to produce from a side cut taken orf from any point in a main iractionating tower, a bottom fraction which is exhausted to any desirable degree, and having a relatively high flash point. It is a further object of this invention to accomplish this operation in an eicient and economical manner.

Another object of this invention is to maire it possible, by proper design and operation of the auxiliary rectifying column, to produce, from a side cut taken oi from any point in the 4main rectifying column, an intermediate cut or fraction, the bottoms of which may be exhausted to any desired degree and to produce at the same time an overhead Which :may be fractionated to any specified end point.

Another object of this invention is to eliminate the disadvantages of passing the unfractionated vapors from the exhausting column directly to the condensing system.

Another object of the invention is tc eliminate the sensitivity, and difficulty of control existing heretofore in other fractionating systems, Wherein large arnounts of steam or other heated gases or vapors were introduced by 'such exhausting operations; and to avoid disturbing the operation, control., or fractionation in the main ractionat ing column.

@ther objects of this invention will be api parent to those skilled in the art, from the fol-1 tically spaced fractionating members 3 and '4, which may be bubble plates or the equivalent thereof; hot oil4 feed line 5; residuum outlet 6; overhead vapor-line 1; reux supply line 8; side cut outlet line I0; divided side cut return or blank plate by-pass II, with regulating valves I3 and I4; auxiliary fractionator reflux return line I5; vapor nozzle I6 in blank plate I1, which may be placed at any point within the height of the column where it is desired to remove the side cut, as through outlet ID and heating medium inlet 39. The side cut, instead of being taken from a special blank plate, such as said blank plate I1, may be taken directly from any ordinary fractionating plate.

The auxiliary rectifying column I8 consists of exhausting section I3 and fractionating column 20 as a unit, separated by blank plate 2I with vapor nozzle 22 therein, and vertically spaced fractionating elements 23 and 24. The fractionating elements may be of the bubble plate type or equivalent, as in the main fractionating tower. The connections to the auxiliary rectifying column are: side cut inlet 25, overhead vapor outlet 26, reflux inlet 21, residual fraction and reflux return outlet 28, heating agent inlet 29 and bottoms outlet 30. Numerals 3I and 32 designate partial and nal condensers respectively. Pumps 33 and 34 return a portion of the condensate from the condensers 3| and 32 respectively to the fractionating columns for reflux. The excess light oil condensate, not used for reflux, flows to the light distillate storage through line 35. Line 35 is an additional point `of introduction for reux which may be supplied from any suitable external source. Heat exchanger 31 may be employed to supply heat to the side cut prior to its introduction into the exhausting column. Residuum may be run prior to storage, through residuum cooler 38.

In operation, the heated oil is introduced into the main fractionating tower near the bottom through inlet 5. The vapors rise in the tower countercurrent to descending reflux oill through fractionating members 3 and 4 spaced vertically throughout the height of the tower. The said descending reux in the tower is in approximate equilibrium with the ascending vapors, both of which vary in composition from top to bottom, i. e., the descending reflux varies from a high ratio of light to heavy components at the top, to a high ratio of heavy to light components at the bottom. Blank plate I1 is accordingly placed in any position relative to the top and bottom of the column where the side cut desired to be drawn off is of the proper composition. A number of such plates may be used, or the bubble plates may be so designed that any number of them may be used to draw off a number of different side cuts, each for separate treatment. The reflux so trapped on a blank plate such as I1 is withdrawn through line I0 and is divided, a portion thereof being introduced as a side cut into the auxiliary fractionating column through line 25, and the balance of the reflux being returned to the lower stages of the main fractionating column through by-pass II. Reflux for the main fractionating tower is introduced at the top through line 8 by pump 33, which pump draws upon the accumulated overhead condensate in the reflux drum supplied by the partial condenser 3|. The bottoms are Withdrawn from the main fractionating tower through line 6 and either run directly through cooler 38 to the residuum storage or through heat exchanger 31 prior to cooling.

The side cut is introduced through line 25 into the exhausting section I9 of the auxiliary rectifying column I8 at a point below the blank plate 2i, where it flows downward V'through plates 24 in countercurrent contact with rising heated vapors and/or steam introduced through 29. The side cut is here stripped of its low boiling fractions. The thus exhausted or stripped liquid is removed and run to storage through bottoms outlet 30. This bottoms constitutes the desired fraction of specified high boiling or high flash characteristics.

The vapors of the low boiling constituents removed from the side cut in the exhausting section I9 pass upward through vapor nozzle 22 in blank plate 2| into auxiliary fractionating column 20, and continue upward through fractionating sections 23 therein, in countercurrent contact with downward flowing reflux. Said reflux is introduced at the top through line 21 and is supplied either by means of pump 34 from a portion of the final overhead condensate from condenser 32 or from any other suitable source through line 36.

to storage through line 35.

The overhead vapors from the auxiliary fractionating tower are removed through vapor line 2G, and are condensed-along with the other light vapors from the partial condenser-in the final condenser 32. The auxiliary fractionating column 20 is designed and operated in such a manner that the overhead issuing therefrom will meet the specification, as to end point of the overhead condensate from the main fractionating tower, and can be mixed therewith in the nal condenser without contaminating said condensate with high boiling point fractions. The 'reflux formed in t-he auxiliary fractionation collects on the blank plate 2I and is removed through outlet 28 and returned through line I5 to an early stage in the main fractionating tower.

Steam, superheated steam, or any other medium may be used to supply heat to the bottom of the exhausting section of the rectifying column, such as gases or vapors of any suitable nature; or heat may be applied externally, or through heating coils suitably placed; and/or heat may be applied to the removed reflux oil prior to introduction into the auxiliary exhausting column by such means as heat interchanger 31 or other heating means, such as an externally fired tubular still similar' to still I. Heat may also be added to the main rectiiying tower as indicated at 39 or in the same manner as for the auxiliary rectifying column.

lt will be understood that this invention is not limited to the specific method and apparatus disclosed, since this disclosure is merely illustrative of one method and apparatus which may be employed, but includes any and all processes and apparatus within the scope of my invention, which I-claim to be:

1. A process of fractionating hydrocarbons which comprises withdrawing a portion of the reflux from an intermediate point in a main fractionating column, withdrawing vapors from said fractionating column, passing the withdrawn reflux in countercurrent contact with heated vapors to remove low boiling point components therefrom, fractionating the thus removed low boiling point vapors in countercurrent contact with reflux oil in an auxiliary fractionating co1- The balance of the final over-` head condensate, not used for reflux, is delivered tol umn out of contact with the vapors tetti-,ir from the main iractionatlng column, re urning the said last-mentioned redini oil to the main iractionating column.

2. fi process of iractionating hydrocarloo which comprises withdrawing an rei-lux from a main fractionating column, with.- drawing vapors from the main :iractionating coiurnn, passing the said withdrawn cil in `counoercurrent Contact with td remove low boiling components, thereby yielding an inte:

iediate fraction of higher flash point, irafc'tionating the said removed low boiling components in an auxiliary iractionating column out contact with the vapors withdraw from the main iractionating column, and returning `the reiiux condensate from the said auxiliary :iractionating column to the main fractionating column.

3. A. process of fractionating hydrocarbons which comprises withdrawing a portion o the reflux from an inrmediate point in a main 4iractionating column, withdrawing vapos :from the main fractionating column, passing the withdrawn reflux in countercurrent contact with heated vapors in an auxiliary exhausting column, to remove low boiling components, thereby yielding an intermediate fraction oi higher flash point, ractionating the said removed low boiling point components in countercurrent contact with reflux oil in an auxiliary fractionating column out of contact with the vapors withdrawn from the main fractionating column, thereby yieldingan intermediate overhead fraction of specified end point, and returning the condensatek from the auxiliary fractionating column to the main iractionating column.

4:. A process of fractionating hydrocarbons which comprises withdrawing a portion of the reux from an intermediate portion oi a main fractionating column, withdrawing vapors from the main fractionating column, passing the withdrawn reflux in countercurrent contact with heated vapors in an auxiliary exhausting column to remove the low boiling point components therefrom, thereby yielding an intermediate fraction of higher ash point, fractionating the said removed low boiling point components in countercurrent contact with reflux in an auxiliary fractionating column out of contact with the vapors withdrawn from the main fractionating columnto produce an'intermediate low boiling point over- -head fraction of specified endpoint, condensing the said overhead fraction, withdrawing the said higher flash point fraction fromthe auxiliary exhausting column and returning the trapped reflux condensate from the auxiliary fractionating col-- umn to the main fractionating column.

5. A process of fractionating hydrocarbons which comprises withdrawing reflux from an intermediate point in a main fractionating column, vaporizing and fractionating the withdrawn reflux oil in an auxiliary fractionating column and returningthe reux condensate from the auxiliary fractionating column to a lower stage column the one ...i withcharm.

i" tionating hfdrocarbons dwing a portion. oi the in iractionating mentioned with-i column eelow ou t .e rirst 7. ier `raotienal arising t? l distillation comin combination vapori-zer, a main iracxonating column to condense and. 'ractionate the rom said main c onating column and to transfer said 'withdravni x condensate to said :nliary raporiaer, an auxiliary ractionating co1- umn, means to pass vapors from said auxiliary vaporixer thrnugli said. auxiliary iraotionating column, means to withdraw overhead fractions from said auxiliary iractionating column, and means to transfer reflux condensate from said amiliary ractionating column to a point in the main iractionating column lower therein than the reflux condensate withdrawal means.

8. Apparatus for fractional distillation comprising in combination a vaporizer, a main iractionating column to condense and iractionate the vapors from the vaporizer, an auxiliary vaporizer, means leading from an intermediate point of the main fractionating column to withdraw a portion of the intermediate relliur condensate therefrom and to transfer said withdrawn reflux condensate to said auxiliary vaporizer, an auxiliary fractionating column, means to pass vapors from said auxiliary vaporizer through said auxiliary rac` tionating column, means to withdraw overhead fractions from said auxiliary fractionating column, means to transfer reux condensate from said auxiliary fractionating column to a point in the main fractionating column lower therein than the reflux condensate withdrawal means, and means to withdraw unvaporized reflux condensate from said auxiliary vaporizer.

9. Apparatus for `fractional distillation comprising in combination a vaporizer, a main fractionating column to condense and iractionate the vapors from the vaporizer, an auxiliary exhausting column, means to withdraw a portion of the reflux condensate from said main fractionating column and transfer said reux condensate to said exhausting column, an auxiliary fractionating column and means to transfer vapors from said auxiliary exhausting column to said auxiliary fractionating column, means to conduct the auxiliary reflux condensate from said auxiliary fractionating column to a point in the main fractionating column lower therein than the reflux condensate withdrawal means and means to withdraw exhausted bottoms from the exhausting column and fractionated vapors from the auxiliary fractionating and main fractionating columns.

EARLE W. GARD. 

